Memory devices with enhanced isolation of memory cells, systems including same and methods of forming same

ABSTRACT

Memory cells of a memory device including a variable resistance material have a cavity between the memory cells. Electronic systems include such memory devices. Methods of forming a memory device include providing a cavity between memory cells of the memory device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/563,277, filed Sep. 21, 2009, pending, the disclosure of which ishereby incorporated herein by this reference in its entirety.

TECHNICAL FIELD

The present invention relates to memory cell structures and methods offorming memory cell structures having enhanced isolation of the memorycells for use in non-volatile memory devices including, for example,resistance memory devices and phase change memory devices, to memorydevices formed by such methods, and to systems including such memorydevices.

BACKGROUND

Various types of non-volatile memory devices employ materials that canbe caused to selectively exhibit more than one stable value ofelectrical resistivity. To form a single memory cell (i.e., one bit), avolume of such a material may be provided between two electrodes. Aselected voltage (or current) may be applied between the electrodes, andthe resulting electrical current (or voltage) therebetween will be atleast partially a function of the particular value of the electricalresistivity exhibited by the material between the electrodes. Arelatively higher electrical resistivity may be used to represent a “1”in binary code, and a relatively low electrical resistivity may be usedto represent a “0” in binary code, or vice versa. By selectively causingthe material between the electrodes to exhibit relatively high and lowvalues of electrical resistivity, the memory cell can be selectivelycharacterized as exhibiting either a 1 or a 0 value.

One particular type of such non-volatile memory devices is a phasechange memory device. In a phase change memory cell, the materialprovided between the electrodes is capable of exhibiting at least twomicrostructural phases or states, each of which exhibits a differentvalue of electrical resistivity. For example, the so-called “phasechange material” may be capable of existing in a crystalline phase(i.e., the atoms of the material exhibit relative long range order) andan amorphous phase (i.e., the atoms of the material do not exhibit anyor relatively little long range order). Typically, the amorphous phaseis formed by heating at least a portion of the phase change material toa temperature above the melting point thereof, and then rapidly coolingthe phase change material to cause the material to solidify before theatoms thereof can assume any long range order. To transform the phasechange material from the amorphous phase to a crystalline phase, thephase change material is typically heated to an elevated temperaturebelow the melting point, but above a crystallization temperature, for atime sufficient to allow the atoms of the material to assume therelatively long range order associated with the crystalline phase. Forexample, Ge₂Sb₂Te₅ (often referred to as “GST”) is often used as a phasechange material. This material has a melting point of about 600° C., andis capable of existing in amorphous and crystalline states. To form theamorphous (high resistivity) phase, at least a portion of the materialis heated to a temperature above the melting point thereof by applying arelatively high current through the material between the electrodes (theheat being generated due to the electrical resistance of the phasechange material) for as little as 10 nanoseconds to 100 nanoseconds. Asthe GST material quickly cools when the current is interrupted, theatoms of the GST do not have sufficient time to form an orderedcrystalline state, and the amorphous phase of the GST material isformed. To form the crystalline (low resistivity) phase, at least aportion of the material may be heated to a temperature of above 400° C.,which is above the crystallization temperature and near, but below, themelting point of the GST material, by applying a relatively lowercurrent through the GST material between the electrodes for a sufficientamount of time (e.g., as little as about 30 nanoseconds) to allow theatoms of the GST material to assume the long range order associated withthe crystalline phase, after which the current flowing through thematerial may be interrupted. The current passed through the phase changematerial to cause a phase change therein may be referred to as the“programming current.”

Various memory devices having memory cells comprising variableresistance material, as well as methods for forming such memory devicesand using such memory devices are known in the art. For example, memorycells comprising variable resistance materials and methods of formingsuch memory cells are disclosed in U.S. Pat. No. 6,150,253 to Doan etal., U.S. Pat. No. 6,294,452, U.S. Pat. No. 7,057,923 to Furkay et al.,U.S. Pat. No. 7,518,007 to Seo et al., United States Patent ApplicationPublication No. 2006/0034116 A1 to Lam et al., and United States PatentApplication Publication No. 2006/0152186 A1 to Suh et al. Furthermore,supporting circuitry that may be used to form a memory device comprisingmemory cells having a variable resistance material, as well as methodsof operating such memory devices, are disclosed in, for example, U.S.Pat. No. 6,885,602 to Cho et al., U.S. Pat. No. 7,050,328 to Khouri etal., and U.S. Pat. No. 7,130,214 to Lee.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming what are regarded as embodiments of the presentinvention, the advantages of the embodiments of this invention may bemore readily ascertained from the description of embodiments of theinvention when read in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a cross-sectional schematic view of a portion of an embodimentof a memory device of the present invention illustrating two memorycells therein;

FIG. 2 is a cross-sectional schematic view of a portion of anotherembodiment of a memory device of the present invention illustrating twomemory cells therein;

FIG. 3 is a cross-sectional schematic view of a portion of yet anotherembodiment of a memory device of the present invention illustrating twomemory cells therein;

FIG. 4 is a cross-sectional schematic view of a portion of yet anotherembodiment of a memory device of the present invention illustrating twomemory cells therein;

FIG. 5A is a cross-sectional schematic view of a portion of yet anotherembodiment of a memory device of the present invention;

FIG. 5B is a cross-sectional schematic view of the portion of the memorydevice shown in FIG. 5A taken along section line 5B-5B therein;

FIG. 6 is a cross-sectional schematic view of an embodiment of a memorydevice of the present invention illustrating four memory cells thereinincluding a tie-down contact formation;

FIGS. 7A and 7B are cross-sectional side views of a workpiece andillustrate an embodiment of a method of the present invention that maybe used to form a memory device like that shown in FIG. 1;

FIGS. 8A and 8B are cross-sectional side views of a workpiece andillustrate another embodiment of a method of the present invention thatmay be used to form a memory device like that shown in FIG. 2;

FIGS. 9A and 9B are cross-sectional side views of a workpiece andillustrate yet another embodiment of a method of the present inventionthat may be used to form a memory device like that shown in FIG. 3;

FIGS. 10A and 10B are cross-sectional side views of a workpiece andillustrate yet another embodiment of a method of the present inventionthat may be used to form a memory device like that shown in FIG. 4;

FIGS. 11A-11D are cross-sectional side views of a workpiece andillustrate yet another embodiment of a method of the present inventionthat may be used to form a memory device like that shown in FIGS. 5A and5B;

FIG. 12 is a schematic block diagram illustrating one embodiment of anelectronic system of the present invention that includes a memory devicelike the memory devices shown in FIGS. 1 through 6.

DETAILED DESCRIPTION

The illustrations presented herein are not meant to be actual views ofany particular memory device, memory cell, workpiece, or system, but aremerely idealized representations that are employed to describeembodiments of the present invention. Additionally, elements commonbetween figures may retain the same numerical designation.

As used herein, the term “variable resistance material” means anymaterial capable of exhibiting more than one stable value of electricalresistivity, and hence, conductivity. Variable resistance materials mayinclude, for example, phase change materials (e.g., chalcogenides suchas, for example, Ge₂Sb₂Te₅, Te₈₁Ge₁₅Sb₂S₂, and Sb₂Te₃), colossal magnetresistive films (e.g., Pr_((1-x))Ca_(x)MnO₃ (PCMO), La_((1-x))Ca_(x)MnO₃(LCMO), and Ba_((1-x))Sr_(x)TiO₃), oxide materials (e.g., doped orundoped binary or ternary oxides such as, for example, Al₂O₃, BaTiO₃,SrTiO₃, Nb₂O₅, SrZrO₃, TiO₂, Ta₂O₅, NiO, ZrO_(x), HfO_(x), and Cu₂O),which may have a Perovskite structure, and materials having the generalformula A_(x)B_(y), where B is selected from sulfur (S), selenium (Se),and tellurium (Te), and mixtures thereof, and where A includes at leastone element from Group III-B (B, Al, Ga, In, Tl), Group IV-B (C, Si, Ge,Sn, Pb), Group V-B (N, P, As, Sb, Bi), or Group VII-B (F, Cl, Br, I, At)with one or more dopants selected from noble metal and transition metalelements such as, for example, Au, Ag, Pt, Cu, Cd, In, Ru, Co, Cr, Ni,Mn, and Mo.

As used herein, the terms “distal” and “proximal” describe positions ofelements of the memory device in relation to a substrate upon which thememory device is formed. For example, the term “distal” refers to aposition relatively more distant from the substrate, and the term“proximal” refers to a position in closer relative proximity to thesubstrate.

As used herein, the term “III-V type semiconductor material” means anysemiconductor material predominantly comprised of one or more elementsfrom group IIIB of the periodic table (B, Al, Ga, In, and Ti) and one ormore elements from group VB of the periodic table (N, P, As, Sb, andBi).

As used herein, the term “II-VI type semiconductor material” means anysemiconductor material predominantly comprised of one or more elementsfrom group IIB of the periodic table (Zn, Cd, and Hg) and one or moreelements from group VIB of the periodic table (O, S, Se, Te, and Po).

As used herein, the term “wafer” means any generally planar structurethat includes a semiconductor material such as, for example, silicon,germanium, gallium arsenide, indium phosphide, and other III-V or II-VItype semiconductor materials. Wafers include, for example, not onlyconventional wafers but also other bulk semiconductor substrates suchas, by way of non-limiting example, silicon-on-insulator (SOI) typesubstrates, silicon-on-sapphire (SOS) type substrates, and epitaxiallayers of silicon supported by a layer of base material. Semiconductortype materials may be doped or undoped. Furthermore, when reference ismade to a “wafer” in the following description, previous process stepsmay have been utilized to at least partially form elements or componentsof a circuit or device in or over a surface of the wafer.

FIG. 1 is a cross-sectional schematic view of a portion of an embodimentof a memory device 100 of the present invention. The memory device 100may include an integrated circuit comprising a plurality of memory cells(e.g., a first memory cell 102 and a second memory cell 104). The memorycells 102, 104 may be arranged in an array on or in a substrate. Forexample, the memory cells 102, 104 may be arranged in a plurality ofrows and columns. The substrate may comprise, for example, a materialsuch as glass or sapphire, or the substrate may comprise a full orpartial wafer, which may facilitate processing using conventionalsemiconductor fabrication processes. In some embodiments, the substratemay comprise a dielectric material 118. By way of example and notlimitation, the dielectric materials discussed herein may comprise anoxide material (e.g., SiO₂, Al₂O₃, etc.), a nitride material (e.g.,Si₃N₄, AlN, etc.), or a combination of oxide and nitride materials suchas, for example, an oxynitride material, a re-oxidized oxynitridematerial, or a so-called “oxide-nitride-oxide” (ONO) structure. Thememory cells 102, 104 may have a longitudinal axis extending from theproximal end of the memory cells 102, 104 to the distal end of thememory cells 102, 104.

As shown in FIG. 1, each of the memory cells 102, 104 may furtherinclude a first electrode 106, a second electrode 108, and a volume ofvariable resistance material 110 disposed between the first electrode106 and the second electrode 108. In some embodiments, the variableresistance material 110 may comprise a phase change material. Forexample, the variable resistance material 110 may comprise a phasechange material such as a chalcogenide material. Typical chalcogenidematerials are alloys predominantly comprising tellurium (Te), germanium(Ge), and antimony (Sb) and include, for example, Ge₂Sb₂Te₅,Te₈₁Ge₁₅Sb₂S₂, and Sb₂Te₃ Chalcognide materials may be characterized bythe general chemical formula Te_(a)Ge_(b)Sb_(100-(a+b)), where a is lessthan about eighty five (85) and b is above about eight (8).

In additional embodiments, the variable resistance material 110 maycomprise any of the other variable resistance materials previouslymentioned herein.

In some embodiments, the electrodes 106, 108 may comprise a materialsuch as, for example, W, Ni, tantalum nitride (TaN), Pt, tungstennitride (WN), Au, titanium nitride (TiN), titanium aluminum nitride(TiAlN), or tantalum silicon nitride (TaSiN).

The first electrode 106 of each of the memory cells 102, 104 may bedisposed over and in electrical communication with another conductivematerial 120. The conductive material 120 may be partially disposed in adielectric material 118 and may communicate electrically with conductivelines, additional memory cells, etc. The conductive material 120 alsomay comprise a material such as, for example, W, Ni, tantalum nitride(TaN), Pt, tungsten nitride (WN), Au, titanium nitride (TiN), ortitanium aluminum nitride (TiAlN) among others. The first electrode 106may extend from the conductive material 120 to the volume of variableresistance material 110. In some embodiments, the first electrode 106may be electrically isolated from surrounding structures by anotherregion of dielectric material 114. In some embodiments, the firstelectrode 106 of each of the memory cells 102, 104 may be substantiallysimilar to the conductive material 120 and may comprise a discrete,laterally isolated volume of conductive material such as a metal.

The second electrode 108 may be disposed over and in electricalcommunication with the volume of variable resistance material 110. Thesecond electrode 108 of each memory cell 102, 104 may be substantiallysimilar to the conductive material 120 and may comprise a discrete,laterally isolated volume of conductive material such as a metal. Insome embodiments, the second electrode 108 may simply comprise an areaor region of an elongated laterally extending conductive trace. In someembodiments, the second electrode 108 may comprise a discrete structureextending between two or more memory cells 102, 104. In someembodiments, the first electrodes 106 may comprise nanowires. Suchmemory cells including nanowires are disclosed in, for example, UnitedStates Patent Application Publication No. 2008/0247226 A1 to Liu et al.

As discussed below with reference to FIG. 6, in some embodiments, eachsecond electrode 108 may communicate electrically with a conductive line(not shown) by way of electrical contacts 621, and each first electrode106 also may communicate electrically with another conductive line (notshown) by way of the conductive material 120. In additional embodiments,the second electrode 108 of each of the memory cells 102, 104 may simplycomprise a region or portion of a conductive line, and the memory cells102, 104 need not include a separate conductive line and electricalcontacts 621.

Although not shown in FIG. 1, each of the memory cells 102, 104 also mayinclude an access transistor for selectively accessing the same for readand write operations, as known in the art.

A manner in which the memory cells 102, 104 may be used or characterizedso as to represent either a “0” or a “1” in binary code is brieflydescribed below with reference to FIG. 1. The variable resistancematerial 110 of the memory cells 102, 104 may exist in a first state orphase (i.e., the atoms may be disposed in a particular microstructure),which can be detected by providing a relatively low voltage between thefirst electrode 106 and the second electrode 108 and measuring themagnitude (e.g., amps) of the resulting current passing between thefirst electrode 106 and the second electrode 108 through the variableresistance material 110. By way of example and not limitation, thisfirst state or phase (and, hence, the current magnitude) may be selectedto represent a “1” in binary code.

To change the state or phase of the variable resistance material 110, arelatively high voltage may be provided between the first electrode 106and the second electrode 108 to induce a relatively high current throughthe variable resistance material 110. This relatively high currentflowing through the variable resistance material 110 may be referred toas the programming current and is used to heat at least a portion 112 ofthe volume of variable resistance material 110 to a sufficienttemperature to cause a change in the state or phase of the portion 112of the variable resistance material 110, as shown in FIG. 1. The portion112 of the variable resistance material 110 then may exhibit anelectrical resistivity (and, inversely, a conductivity) in the secondstate or phase that differs from the electrical resistivity in the firststate or phase. As a result, the presence of the second state or phasecan be detected by again providing a relatively low voltage between thefirst electrode 106 and the second electrode 108 and measuring themagnitude (e.g., amps) of the resulting current passing between thefirst electrode 106 and the second electrode 108, which will bedifferent from the magnitude of the measured current when the portion112 of the variable resistance material 110 is in the first state orphase. By way of example and not limitation, this second state or phase(and, hence, the second current magnitude) may be selected to representa “0” in binary code.

The heat generated in the variable resistance material 110 as theprogramming current is passed therethrough by the electrodes 106, 108 isdue to the electrical resistance of the variable resistance material110. Furthermore, the amount of heat generated in the portion 112 of thevariable resistance material 110 is at least partially a function of thecurrent density in the portion 112 of the variable resistance material110. For a given current passing through the variable resistancematerial 110 between the first electrode 106 and the second electrode108, the current density in the variable resistance material 110 is atleast partially a function of the size (e.g., cross-sectional area) ofthe smaller of the electrodes 106, 108. By using a first electrode 106having a relatively small size, the current density in the portion 112of the variable resistance material 110 is increased, and theprogramming current required to cause a phase change in the portion 112of the variable resistance material 110 is reduced. By decreasing therequired programming current, the energy required to operate the memorydevice 100 may be decreased. As a result, memory devices 100 having arelatively smaller first electrode may be operated using less powerrelative to memory devices having a relatively larger first electrode.

Referring still to FIG. 1, the memory cells 102, 104 may include yetanother region of dielectric material, which is referred to herein as apassivation material 116. As used herein, the term “passivationmaterial” means and includes any dielectric material that is used toelectrically, physically or electrically and physically protect orisolate another material. Similar to the dielectric materials discussedabove, the passivation material 116 may comprise, for example, an oxidematerial (e.g., SiO₂, Al₂O₃, etc.), a nitride material (e.g., Si₃N₄,AlN, etc.), or a combination of oxide and nitride materials. Thepassivation material 116 may be disposed over a portion of the memorycells 102, 104. For example, the passivation material 116 may bedisposed over a portion of the first electrode 106, a portion of thesecond electrode 108, and a portion of the dielectric material 114surrounding the volume of variable resistance material 110. As shown inFIG. 1, in some embodiments, the passivation material 116 may besubstantially conformal on, and substantially surround, the exposedportions of the first electrode 106, the second electrode 108, and thedielectric material 114 surrounding the volume of variable resistancematerial 110. The passivation material 116 may be formed on a portion ofthe memory cells 102, 104 as an at least substantially conformable layerhaving an average thickness of between about two nanometers (2 nm) andabout one thousand nanometers (1,000 nm).

In some embodiments, the passivation material 116 may electricallyisolate the memory cells 102, 104 from each other and from additionalsurrounding memory cells. In some embodiments, the passivation material116 may form a barrier around the memory cells 102, 104 to protect thematerials of the memory cells 102, 104. For example, the passivationmaterial 116 may be formed on the memory cells 102, 104 at relativelylow temperature (e.g., 200° C.). The passivation material 116 mayprotect the memory cells 102, 104 by preventing the volume of variableresistance material 110 from evaporation or sublimation that may becaused by subsequent processing at relatively higher temperature (e.g.,about 300° C. or more). In some embodiments, the passivation material116 may also partially inhibit impurities (e.g., oxygen) from diffusinginto the volume of variable resistance material 110 of the memory cells102, 104.

The memory device 100 may include a cavity 122 disposed between thememory cells 102, 104. As used herein a “cavity” means an area or regionsubstantially devoid of solid material. For example, the cavity 122 maycomprise an area separating adjacent memory cells 102, 104. The cavity122 may, for example, contain a vacuum (i.e., a vacuum cavity), a gas, aliquid, etc. As used herein, the term “vacuum” means a space within thecavity 122 that is substantially empty of matter and has a pressure of500 torr or less. It is noted that while the embodiment of FIG. 1illustrates a cross-sectional view of the cavity 122 extending betweenthe first memory cell 102 and the second memory cell 102, the cavity122, or cavities, may be disposed over multiple sides of each of thememory cells and may, in some embodiments, substantially surround thememory cells. For example, when a plurality of memory cells are arrangedin a plurality of rows and columns, a cavity, or cavities, may bedisposed over multiple sides of the memory cells extending around eachof the memory cells, between each memory cell and the memory cellsadjacent thereto.

The cavity 122 may provide enhanced isolation of the memory cell 102,104. For example, as discussed above, in memory cells 102, 104 includinga volume of variable resistance material 110, a relatively high voltageis used to change the state or phase of the variable resistance material110. The cavity 122 may thermally insulate the variable resistancematerial 110 of a first memory cell 102 from heat generated in anadjacent second memory cell 104. For example, the cavity 122 disposedbetween adjacent memory cells 102, 104 may laterally isolate the heatgenerated in each of the first memory cell 102 and the second memorycell 104. In some embodiments, the cavity 122 may comprise a vacuumhaving a thermal conductively relatively lower than that of air or aconventional dielectric material. The relatively lower thermalconductivity of the vacuum may increase the lateral, thermal isolationof the memory cells 102, 104 by decreasing the amount of heattransferred between the memory cells 102, 104. In some embodiments, thecavity 122 may contain a fluid (e.g., a liquid or gas) having a lowerthermal conductive relative to the thermal conductivity of aconventional dielectric material. The cavity may be at leastsubstantially free of solid matter.

The cavity 122 may have a first dimension D₁₁ between the secondelectrodes 108 of the memory cells 102, 104, and between the volumes ofvariable resistance material 110 of the memory cells 102, 104. In someembodiments, the cavity 122 may have a second dimension D₁₂ greater thanthe first dimension D₁₁. For example, the cavity 122 may extendunderneath the volumes of variable resistance material 110 (i.e., thecavity 122 extends along a proximal side of the volume of variableresistance material 110 toward the dielectric material 114 surroundingthe first electrode 106). By extending between the dielectric material114 surrounding the first electrode 106 of each of the memory cells 102,104, the second dimension D₁₂ of the cavity 122 is greater than thefirst dimension D₁₁. The additional distance (i.e., the second dimensionD₁₂) may provide a larger volume of the cavity 122 between the firstelectrodes 106 of the memory cells 102, 104. The larger volume maydecrease the amount of heat transferred between the first electrodes 106of adjacent memory cells 102, 104.

As shown in FIG. 1, in some embodiments, the cavity 122 may be partiallybounded by the passivation material 116. The cavity 122 may extendbetween the passivation material 116 disposed over the first memory cell102 and the passivation material 116 disposed over the second memorycell 104. Similarly, the first dimension D₁₁ of the cavity 122 may bedefined between passivation material 116 disposed over the secondelectrode 108 and the volume of variable resistance material 110 of eachof the memory cells 102, 104. The second dimension D₁₂ may extendbetween the passivation material 116 disposed over the dielectricmaterial 114 surrounding the first electrode 106 of each of the memorycells 102, 104.

The memory device 100 may further include a dielectric material disposedover (e.g., on) and between distal end portions of the memory cells 102,104. For example, a non-conformal dielectric material 128 (e.g., anon-conformal passivation material) may be disposed over each of thesecond electrodes 108 of the memory cells 102, 104. In some embodiments,the non-conformal dielectric material 128 may be disposed over thepassivation material 116 overlying the second electrode 108 of each ofthe memory cells 102, 104. The non-conformal dielectric material 128 maypartially bound the cavity 122 and, in some embodiments, hermeticallyseal the cavity 122. For example, the non-conformal dielectric material128 may extend between the memory cells 102, 104 to form a distalboundary of the cavity 122 and to seal a vacuum within the cavity. Thesealed cavity 122 may thermally insulate the memory cells 102, 104 fromone another.

As discussed in further detail below, the non-conformal dielectricmaterial 128 may be non-conformal in the sense that the material tendsto have poor step coverage (e.g., the non-conformal dielectric material128 may extend across an opening leading to the cavity 122 withoutsubstantially filling the cavity 122). For example, the non-conformaldielectric material 128 may extend along the second electrode 108 of theeach of the memory cells 102, 104. The non-conformal dielectric material128 may also extend over the cavity 122 across the gap between thesecond electrode 108 of the first memory cell 102 and the secondelectrode 108 of the second memory cell 104, which gap may have a widthof, for example, 0.005 micron to 0.1 micron.

The non-conformal dielectric material 128 may be disposed over thesecond electrode 108 of each of the memory cells 102, 104 and extendacross the cavity 122, or cavities, disposed between the memory cells102, 104 to partially form a distal boundary of the cavity 122. Forexample, the passivation material 116 may form a portion of the boundaryof the cavity 122 and the non-conformal dielectric material 128 may formanother portion of the cavity 122. In some embodiments, the cavity 122may be substantially enclosed. For example, the portions of thepassivation material 116 and the non-conformal dielectric material 128forming the cavity 122 may enclose the cavity 122 (i.e., the interiorspace of the cavity 122 may be sealed from space exterior to the cavity122). As discussed above, in some embodiments, the sealed cavity 122 mayinclude an interior space comprising a vacuum (i.e., the space containedwithin the cavity 122 is substantially empty of matter).

The cavity 122 may also have a height (e.g., dimension D₁₃) extending,for example, between the non-conformal dielectric material 128 and thedielectric material 118. As shown in FIG. 1, in some embodiments, thecavity 122 may extend along lateral sides (i.e., the sides lateral tothe longitudinal axis of the memory cells 102, 104 extending from theproximal ends of the memory cells 102, 104 to the distal ends thereof)of each of the dielectric material 114 surrounding the first electrode106, the second electrode 108, and the volume of variable resistancematerial 110 of each of the memory cells 102, 104. In some embodiments,the dimension D₁₃ of the cavity 122 may extend from the second electrode108 disposed over the distal end of one of the memory cells 102, 104toward the proximal end of the memory cells 102, 104 to the passivationmaterial 116 disposed over the dielectric material 118 between theconductive material 120 of each memory cell 102, 104. In someembodiments, the cavity 122 may extend toward the proximal end of thememory cells 102, 104 past the distal end of the conductive material120. For example, the cavity 122 may extend along the passivationmaterial 116 surrounding the lateral sides of the dielectric material114 surrounding the first electrode 106, the second electrode 108, andthe volume of variable resistance material 110 of each of the memorycells 102, 104, and may extend partially along the passivation material116 surrounding the lateral sides of the conductive material 120.

FIG. 2 is a cross-sectional schematic view of a portion of anotherembodiment of a memory device 200 of the present invention. The memorydevice 200 may be similar to the memory device 100 illustrated anddescribed with reference to FIG. 1, and may include a first memory cell102 and a second memory cell 104 as previously described herein.

In some embodiments, the memory device 200 may not include a separatedielectric material (e.g., the dielectric material 114 shown in FIG. 1)surrounding the first electrode 106; rather the dielectric material 118may surround the conductive material 120 and the first electrode 106.The memory cells 102, 104 may include a passivation material 216disposed over a portion of the memory cells 102, 104. A non-conformaldielectric material 128 may be disposed over the passivation material216 extending around the second electrode 108 and may extend from thesecond electrode 108 of the first memory cell 102 to the secondelectrode 108 of the second memory cell 104.

The memory device 200 may include a cavity 222 disposed between thememory cells 102, 104. Portions of the passivation material 216 andnon-conformal dielectric material 128 may form a boundary of the cavity222 disposed between the memory cells 102, 104. The passivation material216 may extend along the dielectric material 118 surrounding the firstelectrode 106, the second electrode 108, and the volume of variableresistance material 110. As shown in FIG. 2, in some embodiments, thecavity 222 may have a dimension D₂₁ extending between the memory cells102, 104. In some embodiments, the dimension D₂₁ may be substantiallyconstant between the memory cells 102, 104 and along an axis parallel tothe longitudinal axis of the memory cells 102, 104. The cavity 222 mayextend from the passivation material 216 disposed over the dielectricmaterial 118 surrounding the first electrode 106, the second electrode108, and the volume of variable resistance material 110 of the firstmemory cell 102 to the passivation material 216 disposed over thedielectric material 118 surrounding the first electrode 106, the secondelectrode 108, and the volume of variable resistance material 110 of thesecond memory cell 104. In some embodiments, the cavity 222 may extendfrom the second electrode 108 of each of the memory cells 102, 104toward the proximal end of the memory cells 102, 104 to the dielectricmaterial 118 proximate the conductive material 120.

Similar to the cavity 122 described above with reference to FIG. 1, thecavity 222 may be substantially enclosed and may, in some embodiments,include an interior space comprising a vacuum.

FIG. 3 is a cross-sectional schematic view of yet another embodiment ofa memory device 300 of the present invention. The memory device 300 maybe similar to the memory devices 100 and 200 illustrated and describedwith reference to FIGS. 1 and 2, respectively, and may include a firstmemory cell 302 and a second memory cell 304. The memory cells 302, 304may be disposed over and in electrical communication with a conductivematerial 120 disposed over or in a dielectric material 118. The memorycells 302, 304 may include an electrode 306 and a volume of variableresistance material 310. The volume of variable resistance material 310may extend from the conductive material 120 to the electrode 306. Thevolume of variable resistance material 310 may be surrounded by a volumeof dielectric material 114. The electrode 306 may be disposed partiallyon and in electrical communication with the volume of variableresistance material 310. To change the state or phase of a portion 312of the variable resistance material 310, a relatively high voltage maybe provided between the electrode 306 and the conductive material 120 toinduce a relatively high current through the variable resistancematerial 310.

In some embodiments, the conductive material 120 and the volume ofvariable resistance material 310 may comprise an intersectingconfiguration. For example, the conductive material 120 may extend in afirst direction and the volume of variable resistance material 310 mayextend in a second direction substantially perpendicular to the firstdirection. The conductive material 120 and the volume of variableresistance material 310 may form an electrical contact at anintersection point of the two materials. Examples of such memory cellsare disclosed in, for example, United States Patent ApplicationPublication No. 2008/0014733 A1 to Liu.

The memory device 300 may include a non-conformal dielectric material128 disposed over the electrode 306 of each of the memory cells 302,304. The non-conformal dielectric material 128 may extend from theelectrode 306 of the first memory cell 302 to the electrode 306 of thesecond memory cell 304.

The memory device 300 may further include a cavity 322 disposed betweenthe memory cells 302, 304. The electrode 306 of each of the memory cells302, 304, the dielectric material 114 surrounding the volume of variableresistance material 310, the dielectric material 118, the non-conformaldielectric material 128 and, in some embodiments, the conductivematerial 120 may bound the cavity 322 between the memory cells 302, 304.As shown in FIG. 3, the cavity 322 may be similar to the cavity 122shown in FIG. 1. The cavity 322 may have a first dimension D₃₁ extendingbetween the electrode 306 and the volume of variable resistance material310 of each of the memory cells 302, 304. In some embodiments, thecavity 322 may have a second dimension D₃₂ greater than the firstdimension D₃₁. For example, the cavity 322 may extend along a proximalside of the volume of variable resistance material 310 toward thedielectric material 114 surrounding the volume of variable resistancematerial 310. In some embodiments, the cavity 322 may extend between theconductive material 120 of each of the memory cells 302, 304. In someembodiments, the cavity 322 may extend from the electrode 306 disposedover the distal end of one of the memory cells 302, 304 toward theproximal end of the memory cells 302, 304 to the conductive material 120and the dielectric material 118 extending between the conductivematerial 120 of each of the memory cells 302, 304.

In some embodiments, the cavity 322 may be substantially enclosed. Forexample, the portions of the electrode 306, the dielectric material 114surrounding the volume of variable resistance material 310, thedielectric material 118, the non-conformal dielectric material 128 and,in some embodiments, the conductive material 120 forming the cavity 322may enclose the cavity 322. In some embodiments, the sealed cavity 322may include an interior space comprising a vacuum.

FIG. 4 is a cross-sectional schematic view of yet another embodiment ofa memory device 400 of the present invention. The memory device 400 maybe similar to the memory devices 100, 200, and 300 illustrated anddescribed with reference to FIGS. 1, 2, and 3, respectively, and mayinclude a first memory cell 302 and a second memory cell 304 aspreviously described herein.

The memory device 400 may further include a cavity 422 disposed betweenthe memory cells 302, 304. The electrode 306 of each of the memory cells302, 304, the non-conformal dielectric material 128, and the dielectricmaterial 118 may form a boundary of the cavity 422 disposed between thememory cells 302, 304. As shown in FIG. 4, in some embodiments, thecavity 422 may have a dimension D₄₁ extending between the memory cells302, 304. In some embodiments, the dimension D₄₁ may be substantiallyconstant between the memory cells 302, 304 and along an axis parallel tothe longitudinal axis of the memory cells 302, 304. In some embodiments,the cavity 422 may extend from the dielectric material 118 surroundingthe volume of variable resistance material 310 of the first memory cell302 to the dielectric material 118 surrounding the volume of variableresistance material 310 of the second memory cell 304. In someembodiments, the cavity 422 may extend between the dielectric material118 surrounding the conductive material 120 of each of the memory cells302, 304. In some embodiments, the cavity 422 may extend from theelectrode 306 disposed over the distal end of each of the memory cells302, 304 toward the proximal end of the memory cells 302, 304 to thedielectric material 118 proximate the conductive material 120.

Similar to the cavity 322 described above with reference to FIG. 3, thecavity 422 may be substantially enclosed and may, in some embodiments,include an interior space comprising a vacuum.

FIG. 5A is a cross-sectional schematic view of yet another embodiment ofa memory device 500 and FIG. 5B is a cross-sectional schematic view ofthe memory device 500 in FIG. 5A taken along section line 5B-5B.Referring to FIGS. 5A and 5B, the memory device 500 may be similar tothe memory devices 100, 200, 300, and 400 illustrated and described withreference to FIGS. 1, 2, 3, and 4, respectively, and may include a firstmemory cell 502 and a second memory cell 504. Each of the memory cells502, 504 may include a first electrode 506 and a second electrode 508.The electrodes 506, 508 may comprise a conductive material disposed overor in a dielectric material 518. A volume of variable resistancematerial 510 may extend from the first electrode 506 to the secondelectrode 508. The first electrode 506 and the second electrode 508 maybe disposed over a common side of the variable resistance material 510,such as a side of the variable resistance material 510 proximate thedielectric material 518. The volume of variable resistance material 510may be surrounded by a dielectric material 516. To change the state orphase of a portion 512 of the variable resistance material 510, arelatively high voltage may be provided between the first electrode 506and the second electrode 508 to induce a relatively high current throughthe variable resistance material 510.

Conductive material 526 may be disposed over the dielectric material 516of the memory cells 502, 504. For example, structures formed by theconductive material 526 may be disposed over the dielectric material 516at two or more discrete locations proximate to each of the electrodes506, 508. A dielectric material 514 may also be disposed over and may besupported by the conductive material 526. The dielectric material 514may extend between the conductive material 526 disposed proximate toeach of electrodes 506, 508.

The memory device 500 may include a cavity 522 disposed between thememory cells 502, 504 and, in some embodiments, between the electrodes506, 508 of each of the memory cells 502, 504. The electrodes 506, 508,the dielectric material 516, and the conductive material 526 may form aportion of the boundary of a cavity 522. As shown in FIG. 5B, the cavity522 may extend between each of the memory cells 502, 504 and between thedielectric material 514 and the dielectric material 518. The cavity 522may have a dimension D₅₁ extending between the first memory cell 502 andthe second memory cell 504. For example, the cavity 522 may extend fromthe dielectric material 516 surrounding the volume of variableresistance material 510 of the first memory cell 502 to the dielectricmaterial 516 surrounding the volume of variable resistance material 510of the second memory cell 504. In some embodiments, the cavity 522 mayextend from the dielectric material 514 to the dielectric material 518.For example, the cavity 522 may extend along the lateral sides of theconductive material 526, the dielectric material 516 surrounding thevolume of variable resistance material 510, and the electrodes 506, 508.In some embodiments, the cavity 522 may be formed around the entirety ofthe dielectric material 516 surrounding the volume of variableresistance material 510 that is not in contact with the conductivematerial 526 and the electrodes 506, 508.

In some embodiments, the cavity 522 may be substantially enclosed. Forexample, the sealed cavity 522 may include an interior space comprisinga vacuum.

FIG. 6 is a cross-sectional schematic view of an embodiment of a memorydevice of the present invention illustrating memory cells thereinincluding a conductive tie-down contact formation. As shown in FIG. 6,memory cells similar to the memory cells 102, 104, 302, 304, 502, and504 shown in FIGS. 1, 2, 3, 4, 5A, respectively, may form a memorydevice 600 including a tie-down 630. The tie-down 630 may extend throughthe memory device 600 from the substrate (e.g., the dielectric material118) to a surface of the memory device 600 opposing the dielectricmaterial 118 (e.g., the conductive material 634). By the way of exampleand not limitation, the memory cells 102, 103, 104, and 105 may besimilar to those described with reference to FIG. 2. The memory cells102, 103, 104, and 105 may also include an electrical contact 621disposed over each of the memory cells 102, 103, 104, and 105. Forexample, the electrical contact 621 may be disposed over and inelectrical communication with the second electrode 108 of each of thememory cells 102, 103, 104, and 105. In some embodiments, the electricalcontact may include a conductive line and a contact disposed over and inelectrical communication with the second electrode 108 of each of thememory cells 102, 103, 104, and 105. Each second electrode 108 maycommunicate electrically with conductive lines, additional memory cells,etc., by way of electrical contacts 621. The tie-down 630 may extendthrough the dielectric 118 similar to the conductive material 120 andmay also communicate electrically with conductive lines, additionalmemory cells, etc.

An additional dielectric material 628 may be formed on the passivationmaterial 216 overlying the second electrode 108 of each of the memorycells 102, 103, 104, and 105. For example, the additional dielectricmaterial 628 may include a non-conformal dielectric material. As shownin FIG. 6, the additional dielectric material 628 may be disposed overthe passivation material 216 and may fill the area surrounding thetie-down 630 while not filling in the cavities 222 disposed between thememory cells 102, 103, 104, and 105. In some embodiments, the additionaldielectric material 628 may also include a conformal dielectric materialportion disposed over the non-conformal dielectric material portion ofthe additional dielectric material 628 to fill the area surrounding thetie-down 630.

Various methods for forming embodiments of memory devices according tothe present invention, such as the memory devices 100, 200, 300, 400,500, and 600 shown in FIGS. 1, 2, 3, 4, 5A, 6, respectively, aredescribed below. To facilitate description, the methods are describedwith reference to a single or two memory cells (e.g., memory cells 102and 104). In practice, however, a plurality of memory cells may beformed substantially simultaneously, and the memory cells may comprisememory cells of one or of a plurality of memory devices.

In each of the embodiments discussed below, the materials forming thememory device may be formed, grown, or otherwise provided thereon. Thevarious materials may be formed using, for example, depositiontechniques (e.g., chemical vapor deposition (CVD), physical vapordeposition (PVD), atomic layer deposition (ALD), sputtering, thermalevaporation, or plating) and patterning techniques (e.g., masking andetching) known in the art of integrated circuit fabrication. Thedielectric materials comprise an oxide or silicon nitride, and may beformed by chemical vapor deposition, by decomposing tetraethylorthosilicate (TEOS), or by any other process known in the art ofintegrated circuit fabrication.

Additionally, the materials or portions thereof may be removed using,for example, a chemical-mechanical polishing (CMP) process, an etchingprocess, a lift-off process, or a combination thereof. Etching processesmay include, for example, removing portions of the material using a maskand an anisotropic reactive ion (i.e., plasma) etching process andremoving the material using a mask and an isotropic wet chemical etchingprocess. It is noted that the particular composition of the gases usedto generate the reactive ions, the particular composition of thechemical etchant, and the operating parameters of the etching processmay be selected based on the composition of the mask, the material to beetched, and the surrounding materials.

An embodiment of a method that may be used to form, for example, thememory device 100 shown in FIG. 1 is described with reference to FIGS.7A and 7B. Referring to FIG. 7A, memory cells 102, 104 may be formed onand in electrical communication with a conductive material 120 formed onor in a dielectric material 118. The memory cells 102, 104 may include afirst electrode 106, a second electrode 108, and a volume of variableresistance material 110 disposed between the first electrode 106 and thesecond electrode 108. The first electrode 106 may be formed on andextend from the conductive material 120 to the volume of variableresistance material 110. A dielectric material 114 may be formed on theconductive material 120 and may surround the first electrode 106. Anadditional dielectric material 118 (e.g., an oxide material) maysurround the dielectric material 114 and the conductive material 120.The volume of variable resistance material 110 may be formed on thefirst electrode 106 and the dielectric material 114 surrounding thefirst electrode 106. The second electrode 108 may be formed on and inelectrical communication with the volume of variable resistance material110.

As shown in FIG. 7A, a portion of the second electrode 108 and thevolume of variable resistance material 110 may be removed. For example,a portion of the second electrode 108 and the volume of variableresistance material 110 may be removed to form a line stripe structure(i.e., the second electrode 108 and the volume of variable resistancematerial 110 may extend between two or more memory cells 102, 104).Alternatively, a portion of the second electrode 108 and the volume ofvariable resistance material 110 may be removed to form a mesa structure(i.e., portions of the second electrode 108 and the volume of variableresistance material 110 are removed to form a discrete structure on eachof the memory cells 102, 104). The portion of the second electrode 108and the volume of variable resistance material 110 may be removed byprocesses such as, for example, photolithography patterning and etching.By way of example and not limitation, the portions may be formed bypatterning a mask to form an aperture therein at the location at whichit is desired to remove the portions of the second electrode 108 and thevolume of variable resistance material 110. The second electrode 108 andthe volume of variable resistance material 110 may be etched through theaperture in the mask using, for example, an anisotropic reactive ionetching process, to expose the underlying dielectric material 118.

As shown in FIG. 7B, a portion of the dielectric material 118 may alsobe removed using a mask and etch process to form the cavity 122. By wayof example and not limitation, an isotropic wet chemical etching processmay be used to remove a portion of the dielectric material 118. In someembodiments, the dielectric material 118 may comprise an oxide material(e.g., SiO₂) and the dielectric material 114 may comprise a nitridematerial (e.g., Si₃N₄). As shown in FIG. 7B, an etchant with selectivityto the oxide material (i.e., an etchant with a particular compositionconfigured to remove the oxide material at a faster rate as compared tothe removal rate of other materials) may be used to remove the oxide andto expose the dielectric material 114 and, in some embodiments, aportion of the conductive material 120. For example, the etchant may beleft on for approximately eight minutes to etch approximately 80nanometers of the oxide material in a direction proximal end of thememory cells 102, 104. In additional embodiments, the cavity 122 may beformed using a single isotropic wet chemical etching process instead ofa separate anisotropic reactive ion etching process followed by anisotropic wet chemical etching process. In some embodiments, thedielectric material 118 may be etched such that the cavity 122 extendsfrom the distal end of the second electrode 108 of each of the memorycells 102, 104 to the distal end of the conductive material 120.

Referring back to FIG. 1, after etching the dielectric material 118, apassivation material 116 may be formed on (e.g., by a CVD or ALDprocess) the exposed portions of the first electrode 106, the secondelectrode 108, and the dielectric material 114 surrounding the volume ofvariable resistance material 110. A non-conformal dielectric material128 (e.g., an oxide material) may be formed on (e.g., by a CVD or PVDprocess) and extend between the passivation material 116 overlying thesecond electrodes 108 of the memory cells 102, 104. As discussed above,the non-conformal dielectric material 128 may be non-conformal as thematerial tends to have poor step coverage (e.g., the material will tendto be formed in a linear or planar manner and not to deposit or filldepressions or cavities). As appreciated by those skilled in the art,“step coverage” is defined as a ratio of field coverage to sidewallcoverage in the context of deposition over a gap such as a via orcavity. For example, as the non-conformal dielectric material 128 isformed on the second electrodes 108 of the memory cells 102, 104, thenon-conformal dielectric material 128 may extend across a portion of thecavity 122 from the second electrode 108 of the first memory cell 102 tothe second electrode 108 of the second memory cell 104. Stated in otherwords, the non-conformal dielectric material 128 will extend over aportion of the cavity 122 in the gap between the second electrode 108 ofthe first memory cell 102 and the second electrode 108 of the secondmemory cell 104 and will tend not to fill the cavity 122. It is notedthat while the embodiment shown and described with reference to FIG. 1illustrates forming the non-conformal dielectric material 128 over thecavity 122 formed between two memory cells 102, 104, the non-conformaldielectric material 128 may be formed over an array of memory cellscovering the cavity 122 or a plurality of cavities formed throughout thememory cell array.

The non-conformal dielectric material 128 may seal the cavity 122 andmay, in some embodiments, form a vacuum within the cavity 122. Forexample, the memory cell 100 may be formed in a substantial vacuumenvironment. In some embodiments, the non-conformal dielectric material128 may be formed on the memory cells 102, 104 at a relatively lowpressure (e.g., below 100 millitorr). The non-conformal dielectricmaterial 128 may seal the cavity 122 and the vacuum space contained inthe cavity 122, thereby, forming a vacuum within the cavity 122.

An embodiment of a method that may be used to form, for example, thememory device 200 shown in FIG. 2 is described with reference to FIGS.8A and 8B. The memory device 200 may be formed by similar processes asthe memory device 100 described above with reference to FIGS. 1, 7A, and7B, and may include a first memory cell 102 and a second memory cell 104as previously described herein. Referring to FIG. 8A, a volume ofvariable resistance material 110 may be formed on the first electrode106 and the dielectric material 118 and may extend between the firstelectrode 106 of each of the memory cells 102, 104. The second electrode108 may be formed on and in electrical communication with the volume ofvariable resistance material 110.

As shown in FIG. 8B and similar to the memory device 100 shown in FIG.7A, a portion of the second electrode 108, the volume of variableresistance material 110, and the dielectric material 118 may be removedby a pattern and etch process to form the memory cells 102, 104 and thecavity 222. For example, an anisotropic reactive ion etching process maybe used to etch through a portion of the second electrode 108, thevolume of variable resistance material 110, and the dielectric material118. In some embodiments, portions of the second electrode 108, thevolume of variable resistance material 110, and the dielectric material118 may be removed in a single etch process step. In some embodiments,the dielectric material 118 may be etched such that the cavity 222extends from the distal end of the second electrode 108 of each of thememory cells 102, 104 toward the proximal end of the memory cells 102,104 to a depth proximate the distal end of the conductive material 120.

Referring back to FIG. 2, after etching the second electrode 108, thevolume of variable resistance material 110, and the dielectric material118, a passivation material 216 may be formed on (e.g., by a CVD or ALDprocess) the exposed portions of the second electrode 108, thedielectric material 118, and the volume of variable resistance material110. A non-conformal dielectric material 128 (e.g., an oxide material)may be formed on (e.g., by a CVD or PVD process) and extend between thepassivation material 216 overlying the second electrode 108 of each ofthe memory cells 102, 104. The non-conformal dielectric material 128 mayseal the cavity 222 and may, in some embodiments, form a vacuum withinthe cavity 222.

An embodiment of a method that may be used to form, for example, thememory device 300 shown in FIG. 3 is described with reference to FIGS.9A and 9B. Referring to FIG. 9A, memory cells 302, 304 may be formed onand in electrical communication with a conductive material 120 formed onor in a dielectric material 118 (e.g., an oxide material). The memorycells 302, 304 may include an electrode 306, and a volume of variableresistance material 310. The volume of variable resistance material 310may be formed on and extend from the conductive material 120 to theelectrode 306. A dielectric material 114 may be formed on the conductivematerial 120 and may surround the electrode 306. An additionaldielectric material 118 may surround the dielectric material 114 and theconductive material 120. The electrode 306 may be formed on the volumeof variable resistance material 310, the dielectric material 118, andthe dielectric material 114. The electrode 306 may be in electricalcommunication with the volume of variable resistance material 310.

As shown in FIG. 9A and similar to the memory device 100 shown in FIG.7A, a portion of the electrode 306 may be removed (e.g., by aphotolithography patterning and etching process). For example, theelectrode 306 may be etched to expose the underlying dielectric material118.

As shown in FIG. 9B, a portion of the dielectric material 118 may alsobe removed using a mask and etch process to form a cavity 322. By way ofexample and not limitation, an isotropic wet chemical etching processmay be used to remove a portion of the dielectric material 118. In someembodiments, the dielectric material 118 may comprise an oxide material(e.g., SiO₂) and the dielectric material 114 may comprise a nitridematerial (e.g., Si₃N₄). As shown in FIG. 9B, an etchant with selectivityto the oxide material may be used to remove the oxide and to expose thedielectric material 114 and, in some embodiments, a portion of theconductive material 120. In additional embodiments, the portion of theelectrode 306 may be removed and the cavity 322 may be formed using asingle isotropic wet chemical etching process instead of a separateetching processes. In some embodiments, the dielectric material 118 maybe etched such that the cavity 322 extends from the distal end of theelectrode 306 of each of the memory cells 302, 304 to the distal end ofthe conductive material 120.

Referring back to FIG. 3, after etching the dielectric material 118, anon-conformal dielectric material 128 (e.g., an oxide material) may beformed on (e.g., by a CVD or PVD process) and extend between theelectrode 306 of each of the memory cells 302, 304. The non-conformaldielectric material 128 may seal the cavity 322 and may, in someembodiments, form a vacuum within the cavity 322.

An embodiment of a method that may be used to form, for example, thememory device 400 shown in FIG. 4 is described with reference to FIGS.10A and 10B. The memory device 400 may be formed by similar processes asthe memory device 300 described with reference to FIGS. 3, 9A, and 9B,and may include a first memory cell 302 and a second memory cell 304 aspreviously described herein. As shown in FIG. 10A and similar to thememory device 100 shown in FIG. 7A, a portion of the electrode 306 maybe removed (e.g., by a photolithography patterning and etching process).For example, the electrode 306 may be etched to expose the underlyingdielectric material 118.

As shown in FIG. 10B, a portion of the dielectric material 118 may beremoved by a pattern and etch process to form the cavity 422. Forexample, an anisotropic reactive ion etching process may be used to etchthrough a portion of the dielectric material 118. In some embodiments,portions of the electrode 306 and the dielectric material 118 may beremoved in a single etch process step. In some embodiments, thedielectric material 118 may be etched such that the cavity 422 extendsfrom the distal end of the electrode 306 of each of the memory cells302, 304 toward the proximal end of the memory cells 302, 304 to a depthproximate the distal end of the conductive material 120.

Referring back to FIG. 4, after etching the electrode 306 and thedielectric material 118, a non-conformal dielectric material 128 (e.g.,an oxide material) may be formed on (e.g., by a CVD or PVD process) andextend between the electrode 306 of each of the memory cells 302, 304.The non-conformal dielectric material 128 may seal the cavity 422 andmay, in some embodiments, form a vacuum within the cavity 422.

An embodiment of a method that may be used to form the memory device 500shown in FIGS. 5A and 5B is described with reference to FIGS. 11A and11B. Referring to FIG. 11A, each memory cell (e.g., memory cell 502) ofthe memory device 500 may each include a first electrode 506 and asecond electrode 508 formed in a dielectric material 518 (e.g., anitride material). A second dielectric material 519A (e.g., an oxidematerial) may be formed around the electrodes 506, 508. A thirddielectric material 516A (e.g., a nitride material) may be formed aroundthe electrodes 506, 508 and may be substantially flush with the distalends of the electrodes 506, 508. In some embodiments, a portion of thethird dielectric material 516A may be removed after being formed aroundthe electrodes 506, 508 using, for example, a chemical-mechanicalpolishing (CMP) process, a selective etching process, or a lift-offprocess to expose a distal portion of the electrodes 506, 508. Thevolume of variable resistance material 510 may be formed on thedielectric material 516A and may extend from the first electrode 506 tothe second electrode 508. A fourth dielectric material 516B may beformed on the volume of variable resistance material 510. In someembodiments, the third and fourth dielectric materials 516A, 516B maycomprise a similar material (e.g., a nitride material) and may form thedielectric material 516 partially surrounding the volume of variableresistance material 510.

Referring now to FIG. 11B, portions of the dielectric material 516 andthe volume of variable resistance material 510 may be removed (e.g., bya photolithography patterning and etching process). For example, thedielectric material 516 and the volume of variable resistance material510 may be etched to expose a portion of the electrodes 506, 508 and aportion of the underlying second dielectric material 519A. Thedielectric material 516 and the volume of variable resistance material510 may be removed to form a line stripe structure (i.e., as shown inFIG. 5B, the dielectric material 516 and the volume of variableresistance material 510 may extend between the electrodes 506, 508).

An additional dielectric material (e.g., a nitride materialsubstantially similar to the dielectric material 516) may be formed onthe dielectric material 516, the electrodes 506, 508, the volume ofvariable resistance material 510, and the second dielectric material519A to cover the exposed ends of the volume of variable resistancematerial 510 formed by the previous etching process. A portion of thedielectric material 516 may be removed (e.g., by a spacer etch process)to form a line stripe structure, shown in FIG. 11C, which includes thevolume of variable resistance material 510 surrounded by the dielectricmaterial 516.

As shown in FIG. 11D, additional dielectric material 519B (e.g., anoxide material substantially similar to the second dielectric material519A) may be formed on the dielectric material 516, the dielectricmaterial 519A, and the electrodes 506, 508. In some embodiments, thesecond dielectric material 519A, 519B may comprise a similar material(e.g., an oxide material) and may form the dielectric material 519.After forming the dielectric material 519, a portion of the dielectricmaterial 519 may be removed, for example, the dielectric material 516planarized using a chemical-mechanical polishing (CMP). The dielectricmaterial 514 (e.g., a nitride material) may be formed on the dielectricmaterial 516. Conductive material 526 may be formed on dielectricmaterial 516 of the memory cell 502 and may extend through thedielectric material 514 and the dielectric material 519. For example, aportion of the dielectric materials 514, 519 may be removed (e.g., by apatterning and etching process) and the conductive material 526 may beformed to extend from the dielectric material 516 to a distal end of thememory cell 502 (e.g., the distal side of the dielectric material 514).

Referring back to FIGS. 5A and 5B, a portion of the dielectric material519 may be removed by, for example, a pattern and etch process to faunthe cavity 522. In some embodiments the entire dielectric material 519may be removed. For example, an isotropic wet chemical etching processmay be used to remove a portion of the dielectric material 519 byforming a small opening in the dielectric material 514 to expose thedielectric material 519 to the isotropic wet chemical etching process.After the dielectric material 519 is removed, the dielectric material514 found on the conductive material 526 may be supported by theconductive material 526. The cavity 522 formed by the removal of thedielectric material 519 may form a vacuum and may extend between thememory cells 502, 504 and in some embodiments, between the electrodes506, 508 of each of the memory cells 502, 504.

Referring again to FIG. 6, in some embodiments, memory cells similar tothe memory cells 102, 104, 302, 304, and 502 shown in FIGS. 1, 2, 3, 4,and 5A, respectively, may form a memory device 600 including a tie-down630. The memory cells 102, 103, 104, and 105 may be formed in a mannersimilar to the above-described methods. The memory cells 102, 103, 104,and 105 may also include an electrical contact 621 formed on each of thememory cells 102, 103, 104, and 105. For example, the electrical contact621 may be formed on and in electrical communication with the secondelectrode 108 of each of the memory cells 102, 103, 104, and 105. Anadditional dielectric material 628 may be formed on the passivationmaterial 216 overlying the second electrode 108 of each of the memorycells 102, 103, 104, and 105. In some embodiments, the additionaldielectric material 628 may include a non-conformal dielectric material.The non-conformal portion of the dielectric material 628 may fill in thearea surrounding the tie-down 630 while not filling in the cavities 222disposed between the memory cells 102, 103, 104, and 105. In someembodiments, the dielectric material 628 may include a non-conformalportion and a dielectric material. The non-conformal portion may beformed proximate to the memory cells 102, 103, 104, and 105 to seal adistal portion of the cavities 222 while not filling in the cavities222. The dielectric material may be formed on the non-conformal portionof the additional dielectric material 628 and on the passivationmaterial 216 to fill in the area surrounding the tie-down 630 and toform the dielectric material 628.

Memory devices like that shown in FIGS. 1 through 6 may be used inembodiments of electronic systems of the present invention. For example,FIG. 12 is a block diagram of an illustrative electronic system 700according to the present invention. The electronic system 700 maycomprise, for example, a computer or computer hardware component, aserver or other networking hardware component, a cellular telephone, adigital camera, a personal digital assistant (PDA), portable media(e.g., music) player, etc. The electronic system 700 includes at leastone memory device of the present invention, such as one of theembodiments of the memory device 100, 200, 300, 400, 500, and 600 shownin FIGS. 1 through 6. The electronic system 700 further may include atleast one electronic signal processor device 702 (often referred to as a“microprocessor”). The electronic system 700 may, optionally, furtherinclude one or more input devices 704 for inputting information into theelectronic system 700 by a user, such as, for example, a mouse or otherpointing device, a keyboard, a touchpad, a button, or a control panel.The electronic system 700 may further include one or more output devices706 for outputting information (e.g., visual or audio output) to a usersuch as, for example, a monitor, display, printer, speaker, etc. The oneor more input devices 704 and output devices 706 may communicateelectrically with at least one of the memory device 100, 200, 300, 400,500, and 600 and the electronic signal processor device 702.

In view of the above description, some embodiments of the presentinvention include memory devices having memory cells including a cavityextending between the memory cells. In some embodiments, the memorydevices may include a volume of variable resistance material disposedbetween two electrodes. A portion of the memory cells and a passivationmaterial formed over the memory cells may partially form the cavityextending between two memory cells. In additional embodiments, thepresent invention comprises electronic systems that include one or moresuch memory devices. The one or more such memory devices may be inelectrical communication with an electronic signal processor. In otherembodiments, the present invention includes methods of forming suchmemory devices. Such methods may include removing a selected amount ofdielectric material disposed between the memory cells in a memory deviceto form a cavity.

Embodiments of the present invention may be particularly useful informing memory cell structures including enhanced isolation of thememory cells for use in a memory device. Particularly, providingenhanced isolation of the memory cells by a vacuum cavity formed betweenthe memory cells may allow for enhanced thermal isolation of the memorycells. Memory devices, in particular memory devices including a phasechange memory cell, may undergo high temperature changes to alter thestate of the memory cell. The voltage applied to the phase changematerial may bleed from one memory cell to adjacent memory cells and theheat generated in one memory cell may also bleed to the adjacent memorycells. Such thermal and electrical crosstalk between cells my causeunintentional changes in the state of the memory cells. Additionally,forces caused by the thermal expansion and contraction of the memorycell structures during high temperatures changes may introduce stressesinto the structures. Providing a vacuum cavity between the memory cellsmay allow for reduced thermal and electrical crosstalk between the cellsand reduce unintentional state changes in the memory cells andundesirable data loss. Moreover, providing a cavity between the memorycells may allow the cell to freely expand and relax, thereby, reducingthe stress caused by thermal expansion and contraction and improving thestructural integrity of the cells.

While the present invention has been described herein with respect tocertain preferred embodiments, those of ordinary skill in the art willrecognize and appreciate that it is not so limited. Rather, manyadditions, deletions and modifications to the preferred embodiments maybe made without departing from the scope of the invention as hereinafterclaimed, and legal equivalents. In addition, features from oneembodiment may be combined with features of another embodiment whilestill being encompassed within the scope of the invention ascontemplated by the inventors.

1. A method of forming a memory device, the method comprising: removingmaterial disposed between a first memory cell and a second memory cellto form a cavity between the first memory cell and the second memorycell; and forming a dielectric material extending over and between thefirst memory cell and the second memory cell to at least substantiallyenclose the cavity between the first memory cell and the second memorycell.
 2. The method of claim 1, further comprising forming each of thefirst memory cell and the second memory cell to comprise a phase changematerial.
 3. The method of claim 2, wherein removing material disposedbetween the first memory cell and the second memory cell comprisesexposing a portion of an electrode of the first memory cell and exposinga portion of an electrode of the second memory cell.
 4. The method ofclaim 3, wherein removing material disposed between the first memorycell and the second memory cell further comprises exposing a portion ofthe phase change material of the first memory cell and exposing aportion of the phase change material of the second memory cell.
 5. Themethod of claim 4, further comprising forming a passivation material onan exposed portion of the electrode and the phase change material of thefirst memory cell and on an exposed portion of the electrode and thephase change material of the second memory cell.
 6. The method of claim3, wherein removing material disposed between the first memory cell andthe second memory cell further comprises exposing a dielectric materialsurrounding the phase change material of the first memory cell andexposing a dielectric material surrounding the phase change material ofthe second memory cell.
 7. A method of forming a memory device, themethod comprising: at least partially surrounding a volume of variableresistance material of each of a first memory cell and a second memorycell with a dielectric material and at least substantially filling aspace between the volume of variable resistance material of the firstmemory cell and the volume of variable resistance material of the secondmemory cell with the dielectric material; forming a cavity in thedielectric material between the first memory cell and the second memorycell; and enclosing the cavity by providing another dielectric materialover an opening to the cavity between the first memory cell and thesecond memory cell.
 8. The method of claim 7, wherein at least partiallysurrounding the volume of variable resistance material of each of thefirst memory cell and the second memory cell with dielectric materialcomprises: forming a first dielectric material over the volume ofvariable resistance material of each of the first memory cell and thesecond memory cell; and disposing a second dielectric material betweenthe first dielectric material over the volume of variable resistancematerial of the first memory cell and the first dielectric material overthe volume of variable resistance material of the second memory cell. 9.The method of claim 8, wherein forming the cavity in the dielectricmaterial comprises removing a portion of the second dielectric material.10. The method of claim 7, wherein enclosing the cavity comprisesdepositing a non-conformal layer of dielectric material over and betweeneach of the first memory cell and the second memory cell.
 11. The methodof claim 7, wherein forming the cavity in the dielectric materialcomprises etching a portion of the dielectric material.
 12. The methodof claim 10, wherein enclosing the cavity comprises enclosing the cavityat a pressure of 1,000 millitorr or less.
 13. The method of claim 11,wherein etching a portion of the dielectric material comprisesanisotropically etching the portion of the dielectric material.
 14. Themethod of claim 1, further comprising at least partially defining aboundary of the cavity with a portion of the dielectric material. 15.The method of claim 1, wherein forming a dielectric material extendingover and between the first memory cell and the second memory cellcomprises: at least partially surrounding a volume of variableresistance material of each of the first memory cell and the secondmemory cell with the dielectric material; and at least partiallydefining a boundary of the cavity with a portion of the dielectricmaterial surrounding the volume of variable resistance material of eachof the first memory cell and the second memory cell.
 16. The method ofclaim 15, wherein at least partially surrounding the volume of variableresistance material of each of the first memory cell and the secondmemory cell with the dielectric material comprises: disposing a firstdielectric material over the volume of variable resistance material ofeach of the first memory cell and the second memory cell; and disposinga second dielectric material between the first dielectric material overthe volume of variable resistance material of the first memory cell andthe first dielectric material over the volume of variable resistancematerial of the second memory cell.
 17. The method of claim 16, whereinremoving material disposed between a first memory cell and a secondmemory cell to form a cavity between the first memory cell and thesecond memory cell comprises removing a portion of the second dielectricmaterial.
 18. The method of claim 1, wherein forming a dielectricmaterial extending over and between the first memory cell and the secondmemory cell comprises: at least partially surrounding a first volume ofvariable resistance material of the first memory cell with thedielectric material; at least partially surrounding a second volume ofvariable resistance material of the second memory cell with thedielectric material: and forming the cavity to extend from thedielectric material surrounding the first volume of variable resistancematerial to the dielectric material surrounding the second volume ofvariable resistance material.
 19. The method of claim 1, furthercomprising forming the cavity to exhibit an internal pressure of 1,000millitorr or less.
 20. The method of claim 7, further comprising atleast partially defining a boundary of the cavity with a portion of thedielectric material and a portion of the another dielectric material.